1. Field of the Invention
The present invention generally relates to gear form grinding wheels. More specifically, this invention relates to an economical method for forming gears through the use of a bonded diamond or cubic boron nickel (CBN) gear form grinding wheel which is fabricated using another gear form grinding wheel of similar construction.
2. Description of the Prior Art
Grinding wheels are extensively used for numerous fabrication operations including the abrasive machining of gears. Gear grinding wheels are typically of the disk-type variety and have either an abrasive which is dispersed in a binder or resin matrix, or an abrasive which is bonded to the surface of the wheel. One type of disk which represents the present invention is the gear form grinding wheel which is used in a process known as form grinding. In this process, one or more gear teeth are concurrently ground with a grinding wheel whose circumferential surface has a profile which is the inverse of the desired gear tooth profile. In this manner a gear blank can be ground entirely by the gear forming wheel down to the preferred tooth form. Another variation of the disk is a gear-like member whose teeth are intended to mesh with the gear to be manufactured. Such form is known as grinding-generating and is normally limited to abrasive machining of a gear form that previously has been hogged out to roughly the desired gear form.
The grinding wheel abrasives provide the wheel's cutting action. Examples of abrasives suitable for abrasive machining are natural and man-made diamond and cubic boron nitride (CBN), a well known man-made abrasive having a Knoop hardness second only to diamond. CBN is commercially available in many forms, such as an abrasive powder known as Borazon which was developed by the General Electric Company. Both diamond and CBN are noted for their high material removal rates and are typically limited to being bonded to the grinding surface of a metal wheel to improve the structure's shock-resistance.
A typical bonding method well known in the art is to use an electroplating process, such as electroplated nickel, to bond the abrasive to the surface of the wheel. Additionally, to improve the life and material removal rate of such grinding wheels it is known in the art to plate the bonded abrasive grinding surface with titanium nitride. Both electroplated nickel and titanium nitride are well accepted by the industry and are commercially available.
All grinding wheels normally sustain wear through their use. A process referred to as truing is typically used to maintain the grinding wheel to ensure the desired gear tooth form is obtained on the gear blank. Of particular concern is that the grinding wheel surface also becomes dull and "loaded" with chips through use. A process referred to as dressing is used to remove this ineffective surface and expose newly fractured abrasive grains. However, the truing process, and to a much greater extent the dressing process, shorten the life of the grinding wheel, thus requiring replacement of the wheel with a new wheel. Also, dressing of grinding wheels having the abrasive bonded to the grinding surface as described earlier for diamond and CBN wheels is typically discouraged because of the relatively thin film of abrasive deposited on the grinding surface.
Therefore, a general disadvantage of the gear grinding processes known thus far is the continuous requirement for truing and dressing of the grinding wheel. A disadvantage specific to grinding wheels of the type with the abrasive bonded to the grinding surface is the inability to dress the grinding surface, requiring frequent replacement of the wheel. The result can be inefficient and somewhat less than economical method for producing precision ground gears. Efforts have been made to improve truing and dressing techniques as suggested below.
A method for dressing CBN grinding wheels is disclosed in U.S. Pat. No. 4,476,656 to Bovenkerk which relies on using a cemented metal carbide block to improve the grinding wheel surface without excessive removal of the CBN grit. However, this method does not lend itself to effective use with grinding wheels for the manufacture of gear teeth.
A method suitable for dressing "abrasive gear-like precision tools" is disclosed in U.S. Pat. No. 4,677,962 to Loos et al. An improved method for dressing a CBN grinding-generating wheel with a diamond wheel is disclosed in U.S. Pat. No. 4,649,671 to Erhardt et al. However, neither method disclosed applies to gear form grinding wheels and neither suggest a gear manufacturing process.
U.S. Pat. No. 4,697,387 to Wirz shows the use of a gear form grinding wheel for the production of helical toothed gears but does not suggest any reduction in the need for dressing.
Therefore, what is needed is a method for grinding gear teeth with a gear form grinding wheel that is economically more efficient by reducing or eliminating the need for truing and dressing and, therefore, eliminating the requirement for frequent replacement of the wheel, resulting in a reduction in overall expenses associated therewith.